Internal script modification
The templates files are only meant to be used as starting points, you don't need to replace any of them.

In blenders text editor choose the Templates->Python->Operator File Import, modify the contents in the text editor and save it to a file using Text->Save As. The best place to save the file would be in your config folder. You could save it to your desktop and use the Install Addon From File button.

Once you have saved it into your configs addon folder, you can enable the addon in your preferences and use your import addon.